The present invention relates to control systems for moving objects rapidly toward engagement with some sort of stop, and more particularly, to an improved method for operating such a control system.
Although the method of the present invention may be used for operating control systems to move various types of objects toward engagement with various types of stops, the present invention is especially suited for use in operating a control system for an exhaust gas recirculation (EGR) valve as it moves toward its valve seat, and will be described in connection therewith.
EGR systems are employed in automotive vehicles in order to help reduce engine emissions. Such EGR systems typically utilize an EGR poppet valve that is disposed between the engine exhaust manifold and the engine intake manifold and is operable, when in an open position, to permit recirculation of exhaust gas from the exhaust manifold back into the intake manifold.
An actuator is employed for moving the EGR valve between its open and closed positions, because the recirculation of exhaust gasses is appropriate and helpful only at certain times, as is well know to those skilled in the EGR art, and therefore will not be discussed in greater detail hereinafter. EGR valves of the type with which the present invention may be utilized are illustrated and described in U.S. Pat. Nos. 5,937,835 and 6,102,016, both of which are assigned to the assignee of the present invention and incorporated herein by reference.
Electrically actuated EGR valve systems preferably employ software-implemented control logic such that the EGR valve is operating under closed loop control when the EGR valve is being moved from a closed position to an open position and when the EGR valve is being moved from an open position to a closed position. As used herein, the term xe2x80x9cclosed loopxe2x80x9d in regard to the control of the EGR valve will be understood to mean that the control logic is constantly xe2x80x9creadingxe2x80x9d the position of the EGR valve and utilizing the position of the EGR valve as part of the feedback to the control logic. The closed loop control logic controls electrical current to an electric motor which serves as the actuator to control the position of the EGR valve. In such systems, the control logic may generate pulse width modulated (PWM) signals to power the actuator motor and modulate the acceleration and deceleration of the EGR valve, as it moves from one position to another.
For purposes of the present invention, the portion of the total operating cycle of an EGR valve which is of greatest concern is whenever the EGR valve is being moved from an open position to a closed position, in which the EGR valve engages its xe2x80x9cstopxe2x80x9d. Typically, an EGR valve is a poppet valve of the same general configuration and construction as an engine intake or exhaust poppet valve, in which case the xe2x80x9cstopxe2x80x9d is a valve seat of the conventional type. Moving the EGR valve to a closed position is of concern for several reasons, and as is typical, involves a tradeoff. On the one hand, when the control logic commands the actuator to close the EGR valve, it is desirable to close the EGR valve quickly, thus stopping the flow of EGR gasses from the exhaust manifold back into the intake manifold. On the other hand, if the EGR valve is closed too quickly (too high a current to the actuator motor), one likely result would be a dynamic engagement of the EGR valve with its valve seat, thus inducing stresses in the EGR valve itself, and also in the linkage between the electric motor and the EGR valve.
Among the known closing logic arrangements is that illustrated and described in U.S. Pat. No. 6,012,437, assigned to the assignee of the present invention and incorporated herein by reference. The incorporated patent teaches the concept of controlling an EGR valve, during the closing mode, by first controlling the EGR valve under closed loop control until the valve reaches a predetermined distance from the valve seat, and then subsequently, operating the EGR valve under open loop control until the valve engages the valve seat. As used herein, xe2x80x9copen loopxe2x80x9d control will be understood to refer to a control mode in which the logic does not utilize valve position as a feedback to the logic. The purpose of the logic of the above-incorporated patent is to close the valve and hold it closed (sealed relative to its seat) with a known current which remains fairly constant, and within a xe2x80x9csafexe2x80x9d range for the particular application.
It has been observed by the assignee of the present invention, in the course of developing EGR valves and control systems for commercial use, that impact engagement of the EGR valve with its valve seat may occur much more frequently than is desirable. In addition, such impact engagements may involve excessive impact force and stress on the gear train driving the EGR valve.
Accordingly, it is an object of the present invention to provide an improved method for operating a control system to move an object rapidly toward engagement with a stop, in which the improved method overcomes the disadvantages of the generally known prior art.
It is a more specific object of the present invention to provide a method of operating an electrical control system to move an EGR valve rapidly toward engagement with its valve seat, but with almost no likelihood of a premature impact engagement of the EGR valve and its valve seat.
The above and other objects of the invention are accomplished by the provision of an improved method of operating a control system to move an object rapidly toward engagement with a stop, the control system including an actuator operable in response to an electrical position command signal to move the object toward the engagement with the stop.
The improved method of operating the control system comprises the steps of determining if the object is being commanded toward a position within a predetermined distance of the stop. The next step is determining if the object is still at least a predetermined distance from a first position. If the answer to the first step is affirmative and the answer to the second step is affirmative, the next step is commanding the object to the first position, and then determining if the object is within a predetermined tolerance of the first position, and when it is, providing a position command signal corresponding to a substantially unchanging position of the object for a predetermined time period. After the predetermined time period, the next step is continuing the move of the object from the first position toward the engagement with the stop.